Okay, let's see if I understand the question. Correct me if I misunderstood your question.
You've got three mics on the drums and you want them panned. Each mic will be on its own channel on your mixer. Say channel one mic is panned left, channel 2 center and channel 3 right. OK so far?
You also want to use your reverb on all three mics right? And you want the mic that's panned L to have a reverb that's also panned left. And the Center mic to have a reverb that's panned center. Etc.
If I'm on the right track (no pun intended) here's what you can do:
1. Use a stereo reverb.
2. Feed it from TWO auxiliary send outputs from your board. Let's say Aux. 1 sends to the L input of your FX processor. Then Aux. 2 sends to the R input of the same device.
3. On the channel that you want to pan left (in this example channel one), send Aux 1 from that channel to the FX unit. Send channel 2 equal amounts from Aux 1 and Aux 2. And... you guessed it...channel three sends from Aux 2 only. Get it?
4. Make sure of course that you've got a stereo return to your mixer to ensure you get the panning effect.
Hope this helps.
I'm not sure where you're going with your submixing question but at least this may solve one of your problems. Better than a poke in the eye with a sharp stick, huh!
good luck.